Recently, photonic crystals have been attracting notice because these crystals exhibit peculiar spatial distribution or are capable of confining the light in a minute area of the order of submicrons. The photonic crystals are formed by periodically arraying two or more mediums having different dielectric functions. Depending on the spatial dimensions of the periodic arrangement, the photonic crystals exhibiting the periodicity only in a one-dimensional direction are termed one-dimensional photonic crystals, while those exhibiting the periodicity in a two-dimensional direction as well and those exhibiting the periodicity in a three-dimensional direction as well are termed two-dimensional photonic crystals and three-dimensional crystals, respectively. The one-dimensional photonic crystals, formed in many cases by a dielectric multi-layer film, exhibit ‘periodicity’ characteristic of the photonic crystals. Thus, one-dimensional, two-dimensional and three-dimensional photonic crystals, exhibiting the periodic structure, are herein collectively termed photonic crystals.
By introducing line defects into those photonic crystals having a wavelength range devoid of the state of light propagation (photonic band gap), it is possible to produce a waveguide mode in the line defects by light confinement by the photonic band gap, instead of by total light reflection by the differential in the refractive index as in the usual light waveguide (for example, see Non-Patent Document 1).
[Non-Patent Document 1]
J. D. Joannopoulos et al., “Photonic Crystals” (Princeton University Press, 1995)
With the use of this technique, minute light waveguides, enabling sharp bends, may be achieved, and hence the photonic crystals are expected to be used e.g. in a minute optical circuit for communications (for example, see Non-Patent Documents 2 and 3).
[Non-Patent Document 2]
A. Mekis et al., Phys. Rev. B58, 4809 (1998)
[Non-Patent Document 3]
A. Mekis et al., Phys. Rev. Lett. 77, 3787 (1996)
A light waveguide by line defects, introduced into a slab type two-dimensional photonic crystal structure, a Y-branch or a directivity coupler, employing the light waveguide, has been proposed or proven (for example, see Non-Patent Documents 4 to 7).
[Non-Patent Document 4]
S. Y. Lyn et al., Science 282, 274 (1998)
[Non-Patent Document 5]
S. Y. Lyn et al., Opt. Lett. 27, 1400 (2002)
[Non-Patent Document 6]
M. Tokushima et al., Appl. Phys. Lett., 76, 952 (2000)
[Non-Patent Document 7]
H. Yamada et al., submitted to SPIE
For application of the photonic crystals to laser, there is known a single-function optical device of a photonic crystal structure having one of the functions of emission (generation), amplification and modulation of light of a specified wavelength (for example, see Patent Document 1). The light radiated from a light emitting member may be waveguided by the above line defects to be taken to outside the photonic crystal.
There is known an optical device, operating as an optical switch, for controlling the on/off of light incident on the photonic crystal area, by controlling the voltage applied across first and second electrodes, formed to the same pattern on both surfaces of the photonic crystal area (Patent Document 2).
There is also known an apparatus in which the refractive index of photonic crystals is changed by increasing or decreasing the number of electrons in a non-equilibrium state of the photonic crystals, and in which 32 or more lattices are provided along the proceeding direction of the signaling light to enable a sufficiently large change in the light transmittivity, that is, extinction ratio, to be achieved (for example, see Patent Document 3).
There is also known a photonic crystal waveguide in which the separation between the waveguide and a point defect is suitably set to control the proportion of light and electromagnetic waves captured and output (for example, see Patent Document 4).
There is further known an optical device, as a novel device capable of controlling the band structure of the photonic crystals freely, significantly and dynamically, in which the device comprises a structure including at least second and third optical mediums, periodically arranged in a first optical medium at a spacing of the order of a wavelength of the incident light, and in which the conditions of the external fields, applied to the above structure, are changed to vary the refractive index relationships of the first to third optical mediums to render variable the periodicity of spatial distribution of the refractive indices in the above structure (for example, see Patent Document 5).
[Patent Document 1]
JP Patent Kokai Publication No. JP-A-11-330619 (pages 4 and 5 and FIGS. 1, 4, 8 and 9)
[Patent Document 2]
JP Patent Kokai Publication No. JP-P2002-131715A (pages 5 to 7 and FIGS. 1 and 9)
[Patent Document 3]
JP Patent Kokai Publication No. JP-P2002-062554A (page 4 and FIGS. 1 and 9)
[Patent Document 4]
JP Patent Kokai Publication No. JP-P2001-272555A (page 4 and FIG. 1)
[Patent Document 5]
JP Patent Kokai Publication No. JP-P2001-091912A (page 4 and FIG. 1)